1. Field of the Invention
The present invention relates to an image forming apparatus, such as a copying machine, a laser beam printer and so on.
1. Description of the Related Art
Laser printers utilizing the so-called "electrophotographic method" are known as image forming apparatuses. In this method, a photosensitive member is first charged, and then an image is exposed to laser light and developed. Laser printers, having the advantages of providing quality images and performing fast printing operations, are widely used.
The conventional image forming method will now be explained with reference to FIGS. 10 through 12. FIG. 10 is a schematic view of the construction of an image reader for use in color image processing means. The document reading process will now be explained with reference to FIG. 10. A copy key (not shown) of an operational unit is pressed so as to cause a light source 103 to apply light to an original document 101. The light reflected from the document 101 passes through an image forming element array 104 and an infrared-ray cut filter 105 so as to form the document image on a CCD (contact-type CCD color sensor) 106. An optical unit 107 sequentially scans the document 101 placed on a platen 102 while moving in the direction indicated by the arrow shown in FIG. 10 (to the right-hand side of FIG. 10).
As illustrated in FIG. 11, color filters, such as red (R), green (G) and blue (B) filters, corresponding to the respective pixels, are regularly mounted on the CCD 106. Simultaneously with the scanning operation performed on the document 101, electric signals from the CCD 106 are processed by a signal processing circuit 110 shown in FIG. 12.
6B, 6G and 6R shown in FIG. 12 represent signals transmitted from the B, G and R elements mounted on the CCD 106 illustrated in FIG. 11. The B, G and R signals are introduced to an A/D conversion circuit 111 and a density conversion circuit 112 where they are converted to Y.sub.1, M.sub.1 and C.sub.1 digital signals. These signals are further supplied to a circuit 113 for performing black-color extraction and under color removal (UCR) processing where Y.sub.2, M.sub.2, C.sub.2 and Bk.sub.2 signals are generated according to the computation processing expressed by the following equations: EQU Y2=Y1-k.sub.3 min(Y.sub.1, M.sub.1, C.sub.1) EQU M.sub.2 =M.sub.1 -k.sub.3 min(Y.sub.1, M.sub.1, C.sub.1) EQU C.sub.2 =C.sub.l -k.sub.3 min(Y.sub.1, M.sub.1, C.sub.1) EQU Bk.sub.2 =K.sub.1 min(Y.sub.1, M.sub.1, C.sub.1)+k.sub.2
wherein min(Y.sub.1, M.sub.1, C.sub.1) denotes the minimum signal among Y.sub.1, M.sub.1, C.sub.1 signals; and k.sub.1, k.sub.2 and k.sub.3 indicate predetermined coefficients. Subsequently, the Y.sub.1, M.sub.1, C.sub.1 and Bk.sub.2 signals are supplied to a color correction circuit 114 for correcting the spectral distribution of a coloring material used by the color separation filters on the CCD 106 and by the image forming means and are subjected to the computation processing expressed by the following mathematical equations (1): ##EQU1## wherein all to a.sub.44 designate masking coefficients for the color correction. As a result of the above-mentioned computation processing, the Y.sub.3, M.sub.3, C.sub.3 and Bk.sub.3 signals can be visualized by color image forming means (printer) 200, such as a color thermal transfer printer, a color ink jet printer, a color laser printer, etc.
In this manner, according to the conventional technique, the image density and color information on the document image are first read, and the printer is controlled so that the above-mentioned image information can be output as accurately as possible. With this arrangement, good reproducibility of the document image can be enhanced as faithfully as possible, thus achieving high quality of the reproduced images.
There is an increasing demand for even higher reproducibility, more faithful to the document. More specifically, it is highly demanded that the level of glossiness (for example, defined by JIS Z8105-4003, Z8741, P8142 and so on), as well as the image density and color, be reproduced as faithfully as possible from an original document. Conventionally, however, the user sets the degree of glossiness, and also, the number of setting levels of glossiness is very limited, thus making it impossible to achieve accurate reproduction of the level of glossiness in response to the document image.